Development of Highly Ion-Conductive Layered Double Hydroxide As Electrolyte for Solid-State Alkaline Fuel Cells

Abstract

Layered Double Hydroxides (LDHs) have been studied by many researchers for their interesting properties such as ion exchangers, adsorbents, polymer stabilizer, catalyst, and so on. LDHs are well known as anionic clays include anion species and water molecules in the interlayer which consist of positively charged metal hydroxide layers. It was reported that some types of LDHs prepared by co-precipitated method have high OH- conductivity and high performance as electrolyte for Alkaline Fuel Cells (AFCs)1). On the other hand, it is necessary to develop a newly industrial LDH synthesis method which enables to synthesize the particle and the composition uniformly. Homogeneous precipitation method with Urea is one of the general and promising LDH synthesis method to prepare the uniform LDH, in which pH controlled by hydrolysis of Urea. However only CO3 2- type LDHs are formed by the method. Therefore, we developed the new type synthesis named “decarboxylation method” that enables to synthesize LDH with high crystallinity and selective anion species in inner layer from precursor compounds in one pot. Prepared samples were measured by ICP and XRD to determine the compositions and structures, respectively, and observed by FE-SEM. Several intercalated anion (CO3 2-, SO4 2-, NO3 -, and Cl-) type M(II) (Zn2+, Co2+, and Ni2+)-Al(III)LDHs were successfully prepared by the decarboxylation method with highly crystallinity and uniform particle size distribution. The ionic conductivities on prepared LDHs were measured by the AC impedance method. Each NO3 - type LDH has remarkably higher ionic conductivity than another type LDHs. The NO3 - type Zn-Al LDH has highest conductivity than another cation type LDHs, and its conductivity is via 16 mS/cm at 80 oC under R.H.80%. 1) Y. Furukawa, K. Tadanaga, A. Hayashi, and M. Tatsumisago, Solid State Ionics, 192, 185-187 (2011).